Abstract: The paper is concerned with the seasonal variability in rooting capability of×Populus pekinensis stem cuttings and the effect of buds treated with IBA. The endogenous plant hormones are extracted and sisolated from the buds and bark in the different time of the year, and the relaton between plant hortnone level and rooting capability of×Populus pekinensis cuttings has changes in different seasons. However, the cuttings with buds root always better than those without buds. The effect of IBA on rooting capability is different in cuttings with or without buds. It is also changing in different seasons. It is proved by bioassay and GC measurements that the capability of sprouting and rooting of×Populus pekingensis cuttings is closely related to inhibitoris, among the endogenous ABA appears the most effective component.